DEVELOPMENT OF PLANTS 399 



layer forms the pulp and skin, as in the cherry and peach, fruits 

 known as drupes. In many fruits the receptacle becomes fleshy 

 and forms the major portion of the fruit, as in the fig, apple, 

 strawberry, etc., and in the pineapple, the axis of the inflores- 

 cence, as well as parts of the flower, become fleshy. These vari- 

 ous devices serve primarily to preserve the life of the embryo 

 and some of them also assist in distributing the seed. 



When conditions are favorable for growth, which may not be 

 till several years after the seeds have been scattered, the embryo 

 renews its growth. The region below the cotyledons, the hypo- 

 cotyl, or base of the cotyledon itself, elongates and pushes out 

 the root which grows down into the soil, and by a later growth 

 the stem tip, with or without the cotyledons which may remain 

 in the seed, elongates and develops the characteristic stem, 

 branches, leaves and sporophylls of the parent plant. The struc- 

 ture and variations of the mature sporophyte have been presented 

 in the first part of the w r ork (pages 7-145), and will be further 

 considered in the following studies. The terms sporangium, 

 microsporophyll and megasporophyll have been retained up to 

 this point in the work in order to keep clearly before you the 

 progress and relationship of the variations that have attended the 

 evolution of plant life. Now that we have arrived at the highest 

 and largest group of plants, where the sporophylls have become 

 highly modified and curiously associated in clusters called flowers, 

 more familiar names will be used in discussing them, i. e., ovule 

 for the megasporangium and its integument, stamen for micro- 

 sporophyll and pistil for megasporophyll. The terms "carpel" 

 and "pistil" are synonymous when these organs are distinct- 

 i. e., free from one another; but when they cohere to form a 

 compound pistil the term "carpel" is employed to indicate the 

 number of pistils that are united, as in the willow the pistil is 

 composed of two carpels, in the lily of three carpels, etc. 



While the sexual generation, mode of reproduction, and the 

 character of the tissues are very similar in all angiosperms, two 

 very distinct lines of variation or classes are to be noted: A, 

 the Monocotyledones, represented by the grasses, lilies and or- 

 chids; B, the Dicotyledones, represented by our common trees, 

 roses, mints and daisies. 



